A method involving repeated acquisition of behavioral chains will be used to study the acute and chronic effects of various drugs on learning in individual subjects. Pigeons will work for food re-inforcement in a chamber containing three response keys; all three keys are illuminated at the same time by one of four colors. For each session the pigeon's task is to learn a new four-response sequence ("chain") by pecking the correct key in the presence of each color. After learning (within-session error reduction) has stabilized (probably 40-60 sessions), this baseline of repeated acquisition will be used to assess the effects of presession drug administration. For comparison, the drug tests will also be conducted under a performance condition, in which the four-response chain is the same from session to session.